The invention concerns itself with the production of a certain class or definition of three-dimensional fiberboard objects. These objects may be components of assembled products or stand-alone and fully complete products. These fiberboard objects are characterized most often by having one flat surface and having the opposite surface composed of three-dimensional features, such as webs and flanges, which extend away from the flat side. Formation of such articles in prior art requires the use of a porous support member on which are mounted several embodiments of resilient mold inserts. The porous support member may include a screen, which facilitates moisture movement away from the webs of the fiberboard object. Wood fibers are prepared as a thin slurry in the conventional manner and deposited onto the molds to deposit the fibers on top of and between the molds. The water or other carrier fluid is withdrawn through the fiber mat and out the porous support.
A force which is normal to the flat side of the wet mat is next applied to the loose mat. The normal force causes it to become more dense and drives out most of the water. Reaction of the resilient mold, which typically consists of an array of nubs or protuberances, to the normal force produces the three-dimensional formed shapes on the side of the fiber mat opposite the flat face. At this point in the process, the partially de-watered and formed mat can be removed to a separate apparatus for drying, or dried directly within the de-watering apparatus. In the drying process, the normal force is maintained as heat is typically applied primarily to the flat side of the wet mat. The heat vaporizes most of the remaining water and facilitates fiber bonding. After adequate drying and after removal of consolidating pressure, the mat retains its form and has a ratio of strength to weight that is higher than many other wood-based products. The fiberboard product thus formed can be joined with other fiberboard objects to form complete assemblies which also possess high strength-to-weight ratios.
Prior art teaches a method for heating the wet fiber mat by contacting the surfaces of the mat with heated platens. By this method, heat from the platens must be transferred to the interior of the mat by thermal conduction through the fiber mat. Because wood fiber is a poor conductor of heat, little energy from surface heat is available for vaporization of water in the wet interior of the mat as the surface of the mat, which is in contact with the heated platen, dries. Thermal conduction is particularly slow in the web regions of the mat, where heat conduction paths are longest. The result is that drying times can be long, especially for thick products. Slow drying times for these wet fiber mats have prevented efficient, high-speed mass-production of sculptured fiberboard products that are thicker than approximately one-half inch. This limitation has hindered commercialization of a wide range of new applications for sculptured fiberboard in the construction, furniture, material handling, and packaging industries.